In the food industry materials such as egg whites, hydrolyzed milk proteins and soy albumin have been used as aerating agents and heat-setting binders. When properly whipped along with other aqueous foaming or whipping recipe ingredients, the aerating agents permit the ingestion and entrapment of gases therein to provide a foamed or aerated product. These aerating agents must necessarily ingest and entrap an acceptable gas volume within a reasonable whipping time.
A limited and select group of proteinaceous materials have the necessary prerequisital properties to be functionally useful as a whipping agent. In essence, the whipping agent affords the means for achieving an aerated aqueous dispersion comprised of a continuous, homogeneous external aqueous film phase of the water-soluble whipping agent which homogeneously encapsulates a discontinuous internal phase of minute gas bubbles. The water-soluble, film-forming whipping agent provides the means for homogeneously and uniformly ingesting the gas and maintaining the ingested gas uniformly throughout the foamed product. The whipping agent must also necessarily provide a recipe viscosity conducive to the ingestion of gas into the foamed system. The aqueous film-forming, water-retention, film-elongation, cohesiveness, elasticity, compatibility with other recipe additives, etc. properties affect the gas ingestion and entrainment properties of the recipe and contribute to its stabilization against syneresis, collapse and migration while imparting sufficient structural integrity and strength for maintaining its foamed or aerated character.
A particularly successful vegetative protein aerating agent is disclosed in U.S. Pat. No. 3,814,816 by R. C. Gunther. The Gunther vegetable protein aerating agent is typically prepared by initially hydrolyzing an oil-free vegetable protein isolate (preferably soya) with acid or alkali, followed by an enzymatic modification (pepsin) to produce the desired aerating agent.
The relative ability of a foamed product to effectively retain the volume of gas which was initially ingested and entrappd within its foamed structure is frequently referred to as "foam stability."
Comparative to the vegetable protein whipping agents, natural whipping agents (e.g. egg albumin or milk protein) are generally recognized as possessing superior foam stability.
Protein molecules are known to undergo complex association and disassociation and chemical interractions which can adversely affect the overall stability of the aerated product. To compensate against this instability, foam or whip stabilizers are frequently incorporated into the whipping recipe.
Whipping agent stabilizers conventionally used (typically at about 0.01% to about 20.0% by weight of whipping agent dry weight) to facilitate the ingestion and incorporation of gas into whippable compositions include the polyphosphorous acid and salt sequestrants (e.g. meta-, ortho-, pyro-, tri-, tetra-, penta-, hexa-, etc. phosphoric acids and their salts such as those mentioned in the Handbook of Food Additives, CRC, 2nd Edition, pages 661-674 and 744-754). Exemplary phosphorus containing sequestrants for proteins include the ammonium, alkaline earth (e.g. calcium, etc.) alkali (e.g. potassium, sodium, etc.) salts of phosphates and polyphosphates such as trisodium pyrophosphate (TSPP), sodium hexametaphosphate (SHMP), potassium triphosphate (KTP), trisodium phosphate (TSP), tripotassium pentaphosphate (TKPP), disodium phosphate (DSP), sodium tetrapolyphosphate (STPP), mixtures thereof and the like. Such whipping stabilizers improve the protein hydrolyzates dispersibility and solubility in high solids aqueous mediums, increase its water-bonding and gel formation properties, its whipping properties and form complexes with the protein to stabilize the whipped product against syneresis, gas migration and collapse. Other edible hydrophilic film-formers (e.g. gums and/or starches) in minor amounts (e.g. less than 5 parts by weight), such as dextrin, carboxymethyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, alginates, carrageenin, xanthane, pectinates, polyvinylpyrrolidone, gelatin, pregelled starches (e.g. corn starch, potato starch, waxy maize starch, inhibited starches, high-amylose starches) are often utilized to improve upon the whipping and stabilizing properties of whipping recipes.
The most commonly reported leguminous proteins (e.g. soy) are the 2S, 7S, 11S and 15S proteins. Soybeans as a Food Source (CRC Press, Cleveland, Ohio, 1971) reports that the 2S protein (8,000-21,500 M.W.) typically comprises approximately 22%, the 7S (110,000-210,000 M.W.) approximately 37%, the 11S (about 350,000 M.W.) about 31% and the 15S (about 600,000 M.W.) approximately 11% of the total weight of the protein composition of defatted soybean products.
The fractionation and isolation of soy proteins have been extensively reported. U.S. Pat. No. 4,172,828 by Davidson et al. discloses a multiple-staged isolate separation recovery process. The initial soy flake extraction is conducted at pH 6.2-6.8 and a protein fraction is obtained therefrom by cooling the extract. Another isolate fraction may be curded from the initial extract by adjusting the whey fraction to a pH 4.5. Two other soy isolate fractions may be obtained by heating the whey and precipitating an isolate therefrom at a pH 5.3. The remaining recoverable protein is cooled and curded from the whey at a pH 4.5.
A patent by Calvert (U.S. Pat. No. 2,451,659) discloses extracting a soy protein at a pH 4.2-4.8 in the presence of an enzyme inhibiting agent and an oxygen excluding or blanketing agent. A patent issued to Eberl et al., U.S. Pat. No. 2,479,481 discloses a method for producing a substantially undenatured vegetable isolate. According to the Eberl et al. patent, the protein extraction may be suitable conducted at a pH 6.0-9.0. An isolate is curded and recovered from the extract by a pH 4.3-4.9 adjustment with sulfur dioxide. U.S. Pat. No. 3,303,182 discloses an isolation process in which the soy solubles are extracted at a temperature in excess of 80.degree. C. The heat extract is then rapidly cooled to below 5.degree. C. with an isolate being curded therefrom by a pH 4.2-5.0 adjustment.
U.S. Pat. No. 4,188,399 by Shemer discloses a heat-coagulable soy protein product. According to Shemer, the water-soluble protein and carbohydrate constituents when aqueously extracted at a pH 5.1-5.9 in the presence of an antioxidant followed by a pH 4.5 adjustment with phosphoric acid will provide a viscous proteinaceous solution which contains more than 70% of the 7S soy protein fraction. This viscous solution is reportedly useful as a heat-coagulable binder for synthetic and natural meat applications.
British Patent Specification No. 1,377,392 discloses a process for preparing a dry, substantially undenatured, salt-containing soy protein composition. The British patentees report "precipitation of the isolate from aqueous extraction prepared from defatted soy meals in the presence of water-soluble sulfite, bisulfite or dithionate salt, preferably an alkali metal (including ammonium) salt."
A U.S. Pat. No. by Melnychyn (3,630,753) discloses a process for producing a freeze-dried isolate. The process is conducted in the presence of specific types of oxidizing or thiol bearing reagents which are capable of reacting with disulfide linkages at elevated temperatures with the extracted protein being precipitated at pH 4.5.
Other articles reporting means for the separating of the 7S or 11S components include "Purification of the 11S Component of Soybean Protein" by Eldridge et al. (Cereal Chem., Vol. 44, Nov. 1967, pages 645-652), "An Electrophoretic Analysis of Soybean Protein" by Briggs et al., (Cereal Chem., Vol. 27, May 1950, pages 243-257) and "Purification and Characterization of the 11S Component of Soybean Proteins" by Wolf et al., Archieves of Biochemistry and Biophysics, 85, 186-199 (1959).
Numerous other publications disclose enzymatic treatment of vegetable proteins. An early U.S. Pat. No. by John R. Turner (2,489,208) discloses a pepsin modified whipping agent component. An alkaline material such as sodium sulfite, sodium carbonate or sodium hydroxide is used to extract glycinin at a pH 6.4-6.8. The glycinin is then precipitated from the extract (e.g. pH 4.2-4.6) at its isoelectric pH in which sulfur dioxide may be utilized as the adjusting acid. The precipitated glycinin product is then modified with pepsin under temperature and pH conditions conducive to hydrolysis of protein. The glycinin is hydrolyzed with pepsin until its water-solubility is increased to 40-50%. Similarly, U.S. Pat. No. 2,502,482 by Sair et al. reports the enzymatic modification of glycinin with pepsin to produce an isolate wherein at least 60% by weight of the pepsin modified isolate is water-soluble at a pH 5.0.
Puski reports the enzymatic modifying of soy isolates (precipitated at pH 4.5) with Aspergillus oryzae in "Modification of Functional Properties of Soy Proteins by Proteolytic Enzyme Treatment" (Cereal Chem. 52, pages 655-665 (1975)). In this publication the author discloses that the enzyme treatment of soy isolate increased foam expansion but yielded unstable foams.
Several publications also report using saline solutions to extract soy proteins. A publication by A. K. Smith et al. (Jr. American Chemical Society, Vol. 60, June 1938, pages 1316-1320) reports the extraction of soybean meal with pH 6.7 water alone yields more protein extract than an aqueous extraction in the presence of neutral salts.
U.S. Pat. No. 4,131,607 by Petit discloses a two-stage alkaline extraction. The extraction is initially conducted in the presence of sodium sulphite and magnesium salt at a pH 7.0-8.5 which is then increased to a pH 10.0-10.5 to complete the extraction. The protein extracts are then precipitated or curded by adjusting the extract to a pH 4.5-5.5. A patent issued to Martinez et al. (U.S. Pat. No. 3,579,496) similarly discloses a multiple solvent extraction process.
Numerous publications report small amounts of salts will destroy the heat-gelling properties of certain soy isolates which limits their use to recipes essentially free from interfering salt levels.